1. Field of the Invention
The present invention relates to a safety network system for organically connecting a main device such as a machine tool or the like in which operation safety measure is required, to a plurality of safety determining devices such as safety light curtains or the like which determine an operation safety condition or the like, and more particularly, it relates to a safety network system having high reliability in which aged deterioration of a safety determining device itself or the like can be appropriately managed without lowering responsibility of stopping a main device when a danger condition occurs.
2. Description of the Prior Art
In a case where a system having a main device such as a machine tool or the like in which operation safety measure is required and a plurality of safety determining devices such as safety light curtains or the like which determine an operation safety condition or the like is designed, when a network is intervened between those system components and a signal is transmitted or received by communication, the degree of design freedom of the system is improved as compared with a case where those components are directly connected without the network.
More specifically, a network master having charge of an operation of a main device and one or more network slaves having charge of a safety determining device for determining safety which is an operating permission condition of the main device are connected on the network. The network master comprises means for monitoring a determination output of each safety determining device through reception information from each network slave, and stopping the operation of the main device when danger is recognized based on the determination output of the safety determining device. Therefore, any safety determining device determines danger (a human body intrudes in an operation region of the main device or the like), the information (danger/safety) to the effect that is immediately transmitted from the network slave to the network master, and the main device is switched from an operating state to a stopped state by action of the network master.
In order to improve safety of the system, reliability of the safety determining device itself has to be secured. As the safety determining device, there are a safety light curtain, a safety door switch, a safety limit switch and the like. Since aged deterioration occurs in various kinds of transducers such as an output relay, a light emitting element, a light receiving element, a magnetic element and the like contained in the safety determining device, when the operation hours (or energized hours) or the number of operations reaches a predetermined value, the main device is stopped and maintenance such as exchange, repair and check is needed.
In order to appropriately manage a maintenance time of the safety determining device, it is necessary to know an operating condition of the safety determining device which is under the charge of each network slave, on the side of the network master. Therefore, it is necessary that the network slave inform the network master of data for maintenance (data for determining necessity of maintenance) such as the number of on-off times of an output, energized hours, record of malfunction detection and the like of each safety determining device.
When both on/off data (referred to as safety check data hereinafter) which shows whether the output from the safety determining device is safe or dangerous and data for maintenance are constantly transmitted from each network slave to the network master, the operating condition of each safety determining device can be constantly and accurately understood on the side of the network master.
However, since the amount of communication data is increased as the whole of the system, transmission of the safety check data is delayed and when any safety determining device detects human body intrusion or the like and outputs danger determination, response time while the main device is switched from the operating state to the stopped state is lowered.